Greetings,
I don't know enough about the hydralics of WWII armor. Modern armor does not require the engine to be running. Granted the aux pump does work off battries and you will need to recharge eventually but it was not the major voltage eater (that would have been the thermals).
Even if there were no hydralics, the TC could still talk to the Gunner and tell him which way to rotate the turret and how much to elevate or depress the gun to get him in the area of the target.
Once the target is within the sight box, the Gunner takes over.
Regards,